In the industrial production of products product quality plays an increasingly important role. High quality can be achieved on the one hand by appropriately configured, stable production processes. On the other hand, the quality parameters of a product must as exactly as possible be controlled reliably and completely to recognize quality defects at an early stage. In many cases the quality of a surface plays an important role for the product properties. The products may be decorative surfaces such as painting surfaces in motor vehicles, or technical surfaces such as the surface of finely machined metal pistons or bearings.
There are a variety of proposals and concepts to automatically examine such surfaces. Deflectometry is for at least partially reflective surfaces a very promising concept, in which a pattern of lighter and darker areas will be considered over the surface to be inspected. The pattern is shifted relative to the surface. Due to the changes which the inspected areas undergo by the reflection, it is possible to inspect the reflective surface visually. For example, the local slope of a surface point is determined of at least three images with different relative positions of the pattern. With the local inclinations then scratches, pores, bumps, cavities and other dimensional defects can be detected. Also gloss level and scattering properties of the surface can be determined by the deflectometry.
WO 2009/007130 A1 discloses a device wherein the surface is inspected using the deflectometry. All details on the deflectometric evaluation, which are disclosed in WO 2009/007130 A1, are intended to be incorporated herein by reference. The known device includes a tunnel having an inner wall which is provided with a pattern. An article having the surface to be inspected, in this case a motor vehicle, is moved through the tunnel. Meanwhile the surface to be inspected is recorded with multiple cameras. Due to the relative movement of the surface to the pattern the pattern “migrates” from the perspective of the cameras across the surface. For the practical realization of the method, it is advantageous if each surface point to be inspected is recorded at at least four different positions relative to the pattern, wherein the at least four different positions cover exactly one period of the intensity profile. In the process according to WO 2009/007130 A1 this may be achieved in that the moving speed of the motor vehicle is adjusted accurately in the tunnel to the geometric conditions of the pattern in the tunnel.